Switches for a high-voltage which has a role of cutting off a fault current needs to have a performance that is surely capable of cutting off various currents from a small current to a large current. In particular, as for the large current, the following two current cutoff roles must be accomplished.
The one role is to cut off a Short-range Line Fault (SLF) current that has a triangular waveform voltage which has a low absolute value but has a keen change rate, and which appears in the initial stage of rising of a voltage (transient recovery voltage) right after a current zero point. The other role is to cut off a Breaker Terminal short-circuit Fault (BTF) current which has a gentle initial rising of the transient recovery voltage, but which applies a voltage with a high absolute value at a last stage.
In recent years, puffer type switches are widely utilized which have a breaker having connectable and disconnectable contacts, and being placed in a pressure housing filled with an insulative gas like SF6 gas, and which blow the contacts with the insulative gas at the time of a current cutoff operation, thereby extinguishing an arc. According to this scheme, it is necessary to accomplish the two current cutoff roles by a single switch.
Conversely, switches that have breakers which are specialized for the respective current cutoff roles, and which are coupled with each other to accomplish the two current cutoff roles are also developed. That is, those are switches which include a plurality of breakers, and which cause the respective breakers to shear the respective current cutoff roles. According to such switches, the internal space of a pressure housing is separated, a puffer type breaker with an excellent BTF cutoff performance is placed in the one separated space, and a puffer type breaker with an excellent SLF cutoff performance is placed in the other separated space. In addition, both breakers are electrically connected in series.